Hypertension is a pathological increase in blood pressure that is expected to affect around 50% of the human population until 2025 (Ref.: WHO, A Global Brief on Hypertension, World Health Day 2013). Elevated blood pressure (above 135 mmHg systolic) is known to be the major cause of cardiovascular diseases including stroke, heart failure, chronic kidney disease, atherosclerosis and many others. Multiple drugs interfering with different biological regulatory systems have been developed to treat hypertension, among which the ACE inhibitors take over a major role. ACE inhibitors (ACEI) are currently used in the treatment of hypertension, heart failure, different types of nephropathies, and type II diabetes.
Their potency in lowering blood pressure is based on their mechanism of blocking the formation of Angiotensin II (Ang II, Ang 1-8, Ang-(1-8)), which is a peptide hormone of the renin-angiotensin-system (RAS), an important regulatory system for blood pressure and fluid balance.
The RAS, as a peptide hormone system being a crucial therapeutic target in the treatment of cardiovascular diseases, regulates multiple physiologic functions including fluid homeostasis and salt balance. The effector molecules of the RAS, the angiotensin peptides, exert their physiologic effects via specific receptor molecules expressed in a variety of cell types and tissues. Furthermore the RAS is also reported to take over important regulatory roles in the immune system and in cell proliferation, converting the system to a promising target for therapeutic interferences for the treatment of above mentioned pathologic conditions, with a huge potential in the field of immune regulation and neoplastic diseases.
Angiotensin peptides and their metabolites are produced via the concerted action of different angiotensin processing enzymes that are proteases, cleaving off one or more amino-acids either from the C-terminus of precursor molecules (Mono-, Di-, Tricarboxypeptidases), the N-terminus (Mono-, Di, Triaminopeptidases) or cleaving the peptide at an internal position of the molecule (Endopeptidases). Enzymes that have been reported to be involved in angiotensin metabolism include renin, angiotensin-converting-enzyme (ACE), angiotensin-converting-enzyme 2 (ACE2), neutral endopeptidase (NEP), aminopeptidase A (APA), aminopeptidase N (APN), carboxypeptidase a (CPA), thimet oligopeptidase (THOP) or chymase. Further molecular features adding complexity to this important regulatory system include an overlapping substrate specificity of angiotensin processing enzymes involved (e.g.: ACE2 has both, Angiotensin I and Angiotensin II as a substrate) as well as the presence of enzymes carrying out similar reactions (e.g. ACE and chymase both convert Ang I to Ang II). The important role of products and substrates of the enzymatic reactions mediated by some of these enzymes favors them as targets for drugs aimed to interfere with angiotensin mediated physiologic functions.
Aminopeptidases have been shown to be involved in the metabolism and regulation of peptide hormones including angiotensins, bradykinins, vasopressins, endothelins, apelins, dynorphins and many other vasoactive peptides and neuropeptides.
Aminopeptidases have further been described to affect cell growth and cell division leading to therapeutic applications in the field of neoplastic diseases like solid tumors or leukemia. The most prominent aminopeptidase inhibitor in clinical use is Bestatin (Trading name: Ubenimex), which is used in the treatment of solid tumors (Ota et al., Biotherapy 1992). More recently, it has been shown that the inhibition of aminopeptidase A (APA) might be a strategy for treating hypertension, which is based on the mechanism of preventing the formation of Angiotensin III in the brain, which is thought to be a cause of central hypertension (Wright et al., International Journal of Hypertension 2012).    Yang et al. (J Biol Chem 2013, 288 (35): 25638-25645) relates to human aminopeptidase A (APA) crystal structures.    Fournie-Zaluski et al. (PNAS USA 2004, 101 (20): 7775-7780) describes the brain renin-angiotensin system and selective APA inhibitors EC33 and RB150.    Masaaki et al. (Tokai J Exp Clin Med 2013, 38 (2): 62-70) describes antinociceptive effects of [Leu5]enkephalin.    Marc et al. (Archives of Cardiovascular Disease 2009, 102: S114) describes selective APA inhibitors EC33 and RB150.    Eiji Yahiro et al. (Current Pharmaceutical Design, 2013, 19: 3065-3071) describes chymase inhibitors.    Eiji Yahiro et al. (J Cardial Failure, 2005, 11 (9): S271) relates to effects of chymase inhibitors in a hamster heart failure model.    Takai et al. (Eur J Pharmacology, 2004: 1-8) relates to chymase inhibitors in cardiovascular disease and fibrosis.    Chaikuad et al. (BMC Structural Biology 2012, 12 (1): 14) provides a structure of human aspartyl aminopeptidase complexed with a substrate analogue.    Leckie et al. (Curr Med Chem, 2005, 3 (1): 23-32) reviews RAS targeting.    Kitamura et al. (Am J of Physiology, 1999, 276 (5): H1664-H1671) relates to aminiopeptidase P inhibition.
A major challenge for the strategy of preventing the formation of Angiotensin III in the brain by blocking APA is represented by an effective, safe and non-invasive drug delivery. Blockade of APA in the brain leads to favored pharmacologic changes in the central RAS as the formation of the pro-hypertensive peptide Angiotensin III from Angiotensin II is blocked. In contrast to the brain, where Angiotensin III is reported to cause hypertension, Angiotensin II is taking over pro-hypertensive activity in the periphery (tissues and plasma). Therefore, in case that APA is also responsible for formation of Ang 2-8 from Ang 1-8 in the periphery, a complete block of APA in the periphery could lead to unwanted side effects caused by excessive peripheral Ang 1-8 accumulation. Many of the data generated to support the efficacy of the recently developed APA blocker for treating hypertension has been obtained following intra-cerebroventricular (i.c.v.) injection, which is very unlikely to be implemented as a standard anti-hypertensive treatment in humans. Although an inactive pro-drug (RB150) for the APA inhibitor has been developed to overcome this problem, the presence of the active metabolite (EC-33) in the periphery cannot be excluded, as RB150 is known to be a oxidation dependent dimer of EC-33 and many reductive systems are present in human plasma and tissue (e.g. Glutathione-System) that might be capable of reducing the oxidized inactive dimer RB150 to the active metabolite EC-33.
Thus, there is a need for safe and effective treatment of hypertension to avoid cardiovascular complications. The present invention provides pharmaceutical compositions and methods for effectively decreasing blood pressure and for treating diseases related to the RAS.